Genome type of retroviruses — central dogma reversal Retroviruses are characterized by which type of genome inside the virion?

Introduction / Context:
Retroviruses are iconic for using reverse transcriptase to convert their RNA genome into DNA that integrates into the host genome. Recognizing the virion genome type is foundational for understanding their replication strategy and the basis for retroviral vectors.

Given Data / Assumptions:

• Virions contain the genetic material that first enters the host cell.
• Reverse transcription occurs after entry.
• Integration as proviral DNA happens post reverse transcription.

Concept / Approach:
Retroviruses package two copies of a positive-sense single-stranded RNA genome along with reverse transcriptase and other enzymes. After infection, reverse transcription generates double-stranded DNA, which is then integrated as a provirus. Therefore, the genome inside the virion is RNA, not DNA.

Step-by-Step Solution:

Verification / Alternative check:
Classic retroviral biology (e.g., HIV, MLV) demonstrates two RNA strands per virion and packaged RT; only after infection is a DNA intermediate synthesized.

Why Other Options Are Wrong:

• dsDNA/ssDNA: not packaged by retroviruses (parvoviruses package ssDNA; hepadnaviruses have relaxed circular DNA).
• cDNA pre-integrated: integration occurs in host nucleus after reverse transcription.
• Protein-only genome: describes prions, not viruses.

Common Pitfalls:
Confusing the proviral DNA state (host-integrated) with the virion contents.

Final Answer:
RNA genome